Preparation of metal diboride and boron-doped powders

ABSTRACT

A method for producing a metal boride powder includes producing a boriding gas stream from a first powder in a first fluidizing bed reactor, delivering the boriding gas stream to a second fluidized bed reactor through a conduit fluidly connecting the first and second fluidized bed reactors, fluidizing a second powder in the second fluidized bed reactor, mixing the second powder with the boriding gas stream such that a metal boride or boron-doped powder is formed.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. application Ser. No. 16/268,224filed Feb. 5, 2019 for “PREPARATION OF METAL DIBORIDE AND BORON-DOPEDPOWDERS” by R. McGee.

BACKGROUND

The present disclosure generally relates to materials for ultrahightemperature applications and more particularly relates to a method andsystem for producing metal and alloy boride powders for production ofultrahigh temperature ceramics.

Titanium diboride powder, among other metal and alloy boride powders,are promising materials for ultrahigh temperature ceramic applicationsbecause of the properties they exhibit including excellent hardness,high melting point, wear resistance, good thermal and electricalconductivity, and chemical inertness. Conventional manufacture methodsutilize carbothermal reduction, mechanical alloying, sol-gel methods, orhigh temperature synthesis. Carbothermal reduction is a simple andcommonly used method but leads to impurities, unwanted grain size,extensive subsequent processing, and added cost. Titanium diboride(among other metal and alloy borides) is a promising material forengineering applications including abrasive and cutting tools,wear-resistance coating, cemented carbide, cathodes for aluminumelectrolysis cells, and crucibles for holding molten metals. Titaniumalloy/titanium boride reinforced composites offer high stiffness andstrength from reinforcing boride particles and toughness from thetitanium alloy matrix. Other transition metal borides are also promisingmaterials for ultrahigh temperature ceramics applications and aregaining attention for new hypersonic vehicle developments.

Given the growing application for metal boride powders, an improvedmethod of production is needed that overcomes the drawbacks ofconventional production methods.

SUMMARY

In one aspect, a method for producing a metal boride powder includesproducing a boriding gas stream from a first powder in a firstfluidizing bed reactor, delivering the boriding gas stream to a secondfluidized bed reactor through a conduit fluidly connecting the first andsecond fluidized bed reactors, fluidizing a second powder in the secondfluidized bed reactor, mixing the second powder with the boriding gasstream such that a metal boride or boron-doped powder is formed.

In another aspect, an assembly for producing a metal boride powderincludes a first fluidized bed reactor configured to produce a boridinggas stream from a first powder, a second fluidized bed reactor fluidlycoupled to the first fluidized bed reactor through a first conduitconfigured to deliver the boriding gas stream to the second fluidizedbed reactor. The second fluidized bed reactor is configured to mix theboriding gas stream with a second powder, selected from the groupconsisting of metal oxides, metal hydroxides, and alloys to produce ametal boride or boron-doped powder.

The present summary is provided only by way of example, and notlimitation. Other aspects of the present disclosure will be appreciatedin view of the entirety of the present disclosure, including the entiretext, claims and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an assembly for producing metal boride andboron-doped powders.

FIG. 2 is a flow diagram of a method for producing metal boride andboron-doped powders using the system of FIG. 1.

While the above-identified figures set forth embodiments of the presentinvention, other embodiments are also contemplated, as noted in thediscussion. In all cases, this disclosure presents the invention by wayof representation and not limitation. It should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art, which fall within the scope and spirit of theprinciples of the invention. The figures may not be drawn to scale, andapplications and embodiments of the present invention may includefeatures, steps and/or components not specifically shown in thedrawings.

DETAILED DESCRIPTION

Titanium diboride powders, among other metal and alloy boride powders,are promising materials for ultrahigh temperature ceramic applications.The present disclosure seeks to overcome drawbacks of conventionalmanufacture of these powders by combining boriding powders and fluidizedbed technology to produce a boriding gas stream that can be delivered toa second fluidized bed reactor for incorporation into the latticestructure of a metal oxide, metal hydroxide, or alloy powders.

FIG. 1 is a schematic view of dual-fluidized bed reactor assembly 10 forproducing metal boride and boron-doped powders. Assembly 10 includesfirst fluidized bed reactor 12 (hereinafter, “first reactor”),configured to produce a boriding gas stream, and second fluidized bedreactor 14 (hereinafter, “second reactor”), fluidly connected to firstfluidized bed reactor 12 and configured to produce a metal boride orboron-doped powder for use in commercial applications. First and secondreactors 12, 14 are fluidly connected by conduit 16, which can include aplurality of interconnected conduits (unnumbered) and valves 18, 20, 22,24, and which can deliver the boriding gas stream to and from aplurality of optional contaminant scrubbers 26, 38, 30, filters 32, 34,and heat exchangers 36, 38 to produce an uncontaminated and heatedstream of boriding gas suitable for boriding powders of metal oxides,metal hydroxides, and alloys in second reactor 14.

First and second reactors 12 and 14 are known in the art and can be ofsubstantially identical configuration although operated using differentoperational parameters and conditions. For simplicity, first and secondreactors 12 and 14 are described congruently, although it should beappreciated that first and second reactors 12 and 14 can differ and maybe individually optimized to accommodate differing operations.

First and second reactors 12 and 14 include furnace 40 a/40 b, reactorchamber 42 a/42 b, fluidizing gas inlet 44 a/44 b connected to inert gassource 46 a/46 b, and exhaust gas outlet 48 a/48 b. Furnace 40 a/40 bcan be a single-zone or multi-zone furnace as illustrated in theembodiments in FIG. 1, which include three heating zones, each withtemperature controls 50 a/50 b. Multiple heating zones are not necessarybut can provide better temperature control and uniformity of temperaturethroughout reactor chamber 42 a/42 b. Furnace 40 a can be capable ofheating reactor chamber 42 a and maintaining a reactor chambertemperature in excess of 1,300 degrees Celsius for up to 10 hours.Furnace 40 b can generally be operated at a lower temperature but can beconfigured to heat reactor chamber 42 b and maintain a reactor chambertemperature in excess of 850 degrees Celsius for up to 10 hours.

Reactor chamber 42 a/42 b is positioned within a chamber of furnace 40a/40 b. Reactor chamber 42 a/42 b can be suspended from a top of furnace40 a/40 b by tube 52 a/52 b, such that reactor chamber walls are spacedapart from furnace walls to allow fluidizing gas to flow along an outerwall of reactor chamber 42 a/42 b before entering reactor chamber 42a/42 b at a bottom end. Reactor chamber 42 a/42 b has porous plate 54a/54 b on a bottom end which retains a powder within reactor chamber 42a/42 b while allowing a fluidizing gas to enter reactor chamber 42 a/42b.

An inert gas, such as argon or helium, can enter an inner chamber offurnace 40 a/40 b through gas inlet 44 a/44 b at the top of first/secondreactor 12/14. The fluidizing gas is heated in the furnace beforeentering reactor chamber 42 a/42 b. In alternative embodiments,fluidizing gas can also be heated in a preheater (not shown) upstream offurnace 40 a/40 b. Powder within reactor chamber 42 a/42 b can befluidized by the inert gas, mixed, and heated within reactor chamber 42a/42 b. Exhaust gas can exit first and second reactors 12 and 14 throughexhaust gas outlet 48 a/48 b.

First reactor 12 is configured to fluidize and decompose boridingpowders contained in reactor chamber 42 a. Boriding powders can includecommercially available boriding powders, such as EKABOR(R)1. Preferredboriding powders can include but are not limited to mixtures including85% boron carbide (B₄C) and 15% sodium carbonate (Na₂CO₃), 84% B₄C and16% Borax (Na₂B₄O₇), and 100% B₄C. Some boriding powders contain largeamounts of diluent such as silicon carbide (SiC) in addition toactivators like potassium tetrafluoroborate (KBF₄), sodiumtetrafluoroborat (NaBF₄) and ammonium tetrafluoroborate (NH₄BF₄).Diluents can be chosen from either Al₂O₃, SiC, ZrO₂, or varyingcombinations. The presence of SiC can result in competitive simultaneoussiliconizing, while KBF₄ can introduce safety issue due to the potentialfor hydrogen fluoride (HF) formation. For this reason, it may bedesirable to avoid such powders. The presence of small amounts of KBF₄can be handled by including scrubbers 26-30 to remove any HF orfluorinated species produced in the production of the boriding gasstream. Scrubbers 26-30 may be left out of assembly 10 depending on thecomposition of the boriding powder. Alternatively, a bypass conduit 56can cause the boriding gas stream to bypass scrubbers 26-30 for boridingpowders that do not contain KBF₄ or other fluorinated compounds.

Boriding powder can have particle sizes ranging from 10 microns to 1.4millimeters. The fluidizing velocity can be set in accordance withparticle size, with larger particles requiring substantially higherfluidizing velocities of the inert gas stream (e.g., a maximumfluidizing velocity to circulate 10 micron particles can be 0.02 m/s,while a maximum fluidizing velocity to circulate 1.4 millimeterparticles can be 32 m/s). Fluidizing velocity can also be adjusted basedon the temperature of reactor chamber 42 a, with higher fluidizingvelocity generally required at lower temperatures. Fluidizing velocitycan be controlled by valve 58 a and/or mass flow controller 60 a.

The temperature required to decompose boriding powder to produce theboriding gas stream can vary depending on the powder composition.Typically, temperatures between 700 and 1,050 degrees Celsius can causedecomposition, however, higher temperatures, including up to 1,500degrees Celsius, may be necessary for some powder compositions.Temperatures as low as 600 degrees Celsius may also be suitable for thedecomposition of some boriding powder compositions. The boron source(i.e. B₄C, amorphous boron, etc.) decomposes to form gas streamscontaining boron trihalides (e.g. BF₃, BCl₃). For instance, when aboriding mixture containing amorphous boron and NH₄Cl is decomposed, theresulting gas stream can contain HCl, BCl₃, BCl₂H, BCl₂, BH₃, BCl, Cl,and BClH. For complete decomposition, reactor chamber 42 a can be heldat a decomposition temperature for a period of time ranging from 1 to 10hours. The time required for complete decomposition can vary dependingon the temperature of reactor chamber 42 a, amount of material, particlesize, flow conditions, and ramp rate (i.e., time to reach decompositiontemperature). A slower ramp rate can reduce the required hold time oncethe decomposition temperature is reached.

An inline gas chromatograph/mass spectrometer (GC/MS) 62 can be locatedin fluid communication with conduit 16 to sample an exhaust gas fromreactor chamber 42 a. GC/MS 62 can be positioned to sample exhaust gasbetween outlet 48 a of first reactor 12 and inlet 44 b of second reactor14. As illustrated in FIG. 1, GC/MS 62 can be disposed upstream ofscrubbers 26-30, although other locations are contemplated. GC/MS 62 canbe used to detect the presence or absence of the boriding gas stream andprovide such information in real time to a controller or operator.Exhaust gas from first reactor 12 can be delivered to second reactor 14at any time during the decomposition process, including before theboriding gas stream is produced. However, reaction in second reactor 14will not occur until boriding gas is delivered from first reactor 12.GC/MS 62 can be used to determine a start time for reaction in secondreactor 14 as indicated by the presence of boriding gas in the exhaustgas from reactor 12. In alternative embodiments, exhaust gas from firstreactor 12 can be vented through bypass line 64 to an exhaust vent 66thereby bypassing second reactor 14 completely until GC/MS 62 detectsthe presence of the boriding gas stream in conduit 16. Exhaust gas canbe directed through a series of scrubbers 68-72, if necessary, to removecontaminants, before venting to the atmosphere. When the boriding gasstream is detected, bypass conduit 64 can be closed and the boriding gasstream can be directed through conduit 16 to second reactor 14. Beforeentering second reactor 14, the boriding gas stream can be directedthrough scrubbers 26-30 to remove contaminants, as previously discussed,and a series of filters 32, 34 to remove any moisture that may bepresent in the gas stream. Heat exchangers 36, and 38 can be used tocondense water vapor that might be present in the gas stream and toreheat the boriding gas stream, respectively.

The fluidizing velocity of the boriding gas stream may not be sufficientto fluidize powder in second reactor 14. Supplemental fluidizingvelocity can be provided by an inert gas (e.g., argon or helium) frominert gas source 46 b. The velocity of inert gas can be controlled byvalve 58 b and/or mass flow controller 60 b. The inert gas stream andboriding gas stream can be mixed in mixer 74 prior to delivery to secondreactor 14.

Second reactor 14 is configured to fluidize powder capable of producinga metal boride when heated in the presence of the boriding gas stream.Suitable powders can include metal oxides and hydroxides of Group IV, V,and VI metals, including but not limited to titanium dioxide (TiO₂), andalloys. While titanium diboride (TiB₂) has been recognized as apromising material for ultrahigh temperature ceramics applications,other transition metal borides are of interest, including but notlimited zirconium diboride (ZrB₂), hafnium diboride (HfB₂), niobiumdiboride (NbB₂), and tantalum diboride (TaB₂). The risk of sintering canbe increased with use of metal hydroxides and, therefore, use of metaloxide and alloy powders may be preferred. The boriding gas stream ismixed with the powders in reactor chamber 42 b to produce boron-dopedpowders and/or metal boride. The powders in reactor chamber 42 b can bemetal oxides (i.e. MO₃) or metal hydroxides (i.e. H₄MO₄), where M=metal(including alloys), O=oxygen, and H=hydrogen, or can be an alloy (e.g.,titanium, aluminum, cobalt, copper or nickel base). As boriding speciesfrom the boriding gas stream contact the surface of the metal oxide ormetal hydroxide powder particles, the surface oxygen and OH species willgradually be removed and replaced by the boriding species, which adsorbon the surface. This surface functionalization results in “borided”surface, or as referred to herein as a “boron-doped powder.” Theboriding gas will also diffuse into the surface of alloy powders. Asreaction time and temperature increase and the thickness of the surfaceboride layer increases, the boron species begin to diffuse into the bulkstructure of the powder (displacing the bulk oxygen in oxides andhydroxides) to form bulk metal boride powders (referred tointerchangeably herein as metal “diborides”). Reactor chamber 42 b canbe used to produce both boron-doped powders and metal boride.

It will be understood by one of ordinary skill in the art that thedegree of doping or boriding will depend on the operational parameters,including but not limited to reactor temperature, fluidizing velocity,particle size, availability of boriding species (i.e., boriding gasconcentration), and residence time. The boriding gas stream can berecycled through reactor chamber 42 b to optimize the boriding reaction.The boriding gas stream can be recycled from exhaust outlet 48 b back toinlet 44 b through conduit 76. Second reactor 14 can be held at aboriding temperature for a period of time ranging from 1 to 10 hours toallow for complete reaction of the powder in reactor chamber 42 b.Similar to the decomposition of boriding powders, the boriding processtime can vary depending on the temperature of reactor chamber 42 b,amount of material, particle size, flow conditions, and ramp rate.Particle size of powder in reactor chamber 42 b can generally range from5 nm to 2.0 μm. A second inline GC/MS 78 or suitable sensor can beplaced on an outlet conduit from exhaust outlet 48 b of second reactor14 to detect the presence of boriding gas stream and/or byproducts ofthe reaction between the boriding gas stream and metal oxide or metalhydroxide powders (e.g., carbon dioxide or water) to assist indetermining if the reaction is complete and whether or not recycle ofthe exhaust stream should be continued.

First reactor 12 continues to produce the boriding gas stream andprovide the boriding gas stream to second reactor 14 throughout theboriding process. Boriding powder can be added intermittently to reactorchamber 42 a of first reactor 12 or upon completion of decomposition ofavailable powder in reactor chamber 42 a. Second reactor 14 can bemaintained at a boriding temperature even in the absence of a boridinggas stream under inert gas, such that the boriding process can begin assoon as the boriding gas stream becomes available.

FIG. 2 is a flow diagram of method 80 for producing metal borides orboron-doped powders using assembly 10 substantially as described withrespect to FIG. 1. In step 82, B₄C is decomposed in first reactor 12 toproduce a boriding gas stream. As disclosed with respect to FIG. 1, thedecomposition process can take 1 to 10 hours depending on the amount ofmaterial, flow conditions, particle size, temperature of reactor chamber42 a, and ramp rate. In step 84, the boriding gas stream is delivered tosecond reactor 14. Prior to delivery, the boriding gas stream can bepassed through a series of scrubbers and/or filters to removecontaminants and moisture that may be present. If the boriding gasstream does not have a flow velocity sufficient to fluidize powder insecond reactor 14, supplemental inert gas can be delivered to obtain adesired fluidizing velocity in reactor chamber 42 b. The fluidizedpowder is mixed with the boriding gas stream and heated in step 86 toallow boron to diffuse into the lattice structure of the metal oxides,hydroxides, or alloys to form a metal boride or boron-doped powder. Whenthe boriding process is complete, the delivery of the boriding gasstream is discontinued as first reactor 12 is isolated from secondreactor 14 and shut down. In step 90, second reactor 14 is shut down andallowed to cool, reactor chamber 42 b is purged with an inert gas, andthe metal boride or boron-doped powder is removed.

Conventional metal boride powder manufacturing methods can lead toimpurities, unwanted grain size, extensive subsequent processing, andadded cost. Dual fluidized bed reactor assembly 10 overcomes many of thedrawbacks of the conventional processes and can be used to produce highpurity metal borides with optimal mechanical, thermal, and electricalproperties.

Summation

Any relative terms or terms of degree used herein, such as“substantially”, “essentially”, “generally”, “approximately” and thelike, should be interpreted in accordance with and subject to anyapplicable definitions or limits expressly stated herein. In allinstances, any relative terms or terms of degree used herein should beinterpreted to broadly encompass any relevant disclosed embodiments aswell as such ranges or variations as would be understood by a person ofordinary skill in the art in view of the entirety of the presentdisclosure, such as to encompass ordinary manufacturing tolerancevariations, incidental alignment variations, transient alignment orshape variations induced by thermal, rotational or vibrationaloperational conditions, and the like. Moreover, any relative terms orterms of degree used herein should be interpreted to encompass a rangethat expressly includes the designated quality, characteristic,parameter or value, without variation, as if no qualifying relative termor term of degree were utilized in the given disclosure or recitation.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A method for producing a metal boride powder according to an exemplaryembodiment of this disclosure, among other possible things includesproducing a boriding gas stream from a first powder in a firstfluidizing bed reactor, delivering the boriding gas stream to a secondfluidized bed reactor through a conduit fluidly connecting the first andsecond fluidized bed reactors, fluidizing a second powder in the secondfluidized bed reactor, mixing the second powder with the boriding gasstream such that a metal boride powder is formed.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations, additional components, and/or steps:

A further embodiment of the foregoing method can further includefluidizing the boron carbide in a first chamber of the fluidized bedreactor, wherein the first power comprises boron carbide.

A further embodiment of any of the foregoing methods, wherein the secondpowder can be selected from the group consisting of metal oxides andmetal hydroxides.

A further embodiment of any of the foregoing methods can further includeheating the first chamber to a temperature ranging from approximately600 to 1500 degrees Celsius to promote decomposition of the boroncarbide and formation of the boriding gas stream.

A further embodiment of any of the foregoing methods, wherein the firstpowder can have a particle size ranging from approximately 10 microns to1.4 millimeters.

A further embodiment of any of the foregoing methods can further includesampling a first exhaust gas from the first fluidized bed reactor todetect the formation of the boriding gas stream.

A further embodiment of any of the foregoing methods can further includedelivering a mixture of the boriding gas stream and an inert gas to thesecond fluidizing bed reactor to fluidize the second powder.

A further embodiment of any of the foregoing methods can further includerecycling the boriding gas stream from an exhaust outlet of the secondfluidizing bed reactor to an inlet of the second fluidizing bed reactor.

A further embodiment of any of the foregoing methods can further includeheating a second chamber of the second fluidizing bed reactor to atemperature within the range of 500 to 850 degrees Celsius.

A further embodiment of any of the foregoing methods can further includesampling an exhaust gas from the second fluidized bed reactor to detecta product formed in the reaction of the boriding gas stream and thesecond powder.

A further embodiment of any of the foregoing methods can further includediscontinuing supply of the boriding gas stream to the second fluidizedbed reactor, cooling the second fluidized bed reactor, and purging thesecond fluidized bed reactor with an inert gas.

An assembly for producing a metal boride powder according to anexemplary embodiment of this disclosure, among other possible thingsincludes a first fluidized bed reactor configured to produce a boridinggas stream from a first powder, a second fluidized bed reactor fluidlycoupled to the first fluidized bed reactor through a first conduitconfigured to deliver the boriding gas stream to the second fluidizedbed reactor. The second fluidized bed reactor is configured to mix theboriding gas stream with a second powder, selected from the groupconsisting of metal oxides and metal hydroxides to produce a metalboride powder.

The assembly of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations, and/or additional components:

A further embodiment of the foregoing assembly, wherein the first powdercan compromise boron carbide.

A further embodiment of any of the foregoing assemblies, wherein thefirst powder can have a particle size ranging from approximately 10microns to 1.4 millimeters.

A further embodiment of any of the foregoing assemblies can furtherinclude a first inert gas source fluidly coupled to a first reactorchamber of the first fluidized bed reactor to fluidize the first powderin the first reactor chamber.

A further embodiment of any of the foregoing assemblies can furtherinclude a second inert gas source fluidly coupled to a second reactorchamber of the second fluidized bed reactor to fluidized the secondpowder in the second reactor chamber.

A further embodiment of any of the foregoing assemblies, wherein thefirst reactor chamber is configured to be heated to a temperatureranging from 600 to 1500 degrees Celsius to promote decomposition of theboron carbide and production of the boriding gas stream.

A further embodiment of any of the foregoing assemblies can furtherinclude a bypass conduit fluidly connecting the first conduit to anexhaust vent, thereby bypassing the second fluidized bed reactor, and avalve configured to alternatively direct gas from the first fluidizedbed reactor to the exhaust vent and to the second fluidized bed reactor.

A further embodiment of any of the foregoing assemblies can furtherinclude an in-line gas chromatography/mass spectrometer (GC/MC)configured to sample a gas stream in the first conduit to detect thepresence of the boriding gas stream.

A further embodiment of any of the foregoing assemblies can furtherinclude an in-line gas chromatography/mass spectrometer (GC/MS)configured to sample a gas stream in an exhaust outlet from the secondfluidized bed reactor to detect a product formed in the reaction of theboriding gas stream and the second powder.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. An assembly for producing a metal boride powder, the assemblycomprising: a first fluidized bed reactor configured to produce aboriding gas stream from a first powder; a second fluidized bed reactorfluidly coupled to the first fluidized bed reactor through a firstconduit configured to deliver the boriding gas stream to the secondfluidized bed reactor, wherein the second fluidized bed reactor isconfigured to mix the boriding gas stream with a second powder selectedfrom the group consisting of metal oxides, metal hydroxides, and alloys,to produce a metal boride powder or boron-doped powder.
 2. The assemblyof claim 1, and further comprising a first inert gas source fluidlycoupled to a first reactor chamber of the first fluidized bed reactor tofluidize the first powder in the first reactor chamber.
 3. The assemblyof claim 2, and further comprising a second inert gas source fluidlycoupled to a second reactor chamber of the second fluidized bed reactorto fluidize the second powder in the second reactor chamber.
 4. Theassembly of claim 3, wherein the first reactor chamber is configured tobe heated to a temperature ranging from 600 to 1500 degrees Celsius topromote decomposition of the first powder and production of the boridinggas stream.
 5. The assembly of claim 4, wherein the first powdercomprises boron carbide.
 6. The assembly of claim 5, wherein the firstpowder has a particle size ranging from approximately 10 microns to 1.4millimeters.
 7. The assembly of claim 1, and further comprising: abypass conduit fluidly connecting the first conduit to an exhaust vent,thereby bypassing the second fluidized bed reactor; and a valveconfigured to alternatively direct gas from the first fluidized bedreactor to the exhaust vent and to the second fluidized bed reactor. 8.The assembly of claim 7, and further comprising a scrubber in fluidcommunication with the first conduit and positioned in fluid connectionbetween the first fluidizing bed reactor and the exhaust vent.
 9. Theassembly of claim 7, and further comprising a scrubber positioned influid connection between the first fluidizing bed reactor and the secondfluidizing bed reactor.
 10. The assembly of claim 1, and furthercomprising an in-line gas chromatography/mass spectrometer (GC/MC)configured to sample a gas stream in the first conduit to detect thepresence of the boriding gas stream.
 11. The assembly of claim 10, andfurther comprising an in-line gas chromatography/mass spectrometer(GC/MS) configured to sample a gas stream in an exhaust outlet from thesecond fluidized bed reactor to detect a product formed in the reactionof the boriding gas stream and the second powder.
 12. The assembly ofclaim 1, and further comprising a recycle conduit fluidly connecting anexhaust outlet of the second fluidizing bed reactor to an inlet of thesecond fluidizing bed reactor.
 13. The assembly of claim 1, and furthercomprising a filter in fluid communication with the first conduit andpositioned in fluid connection between the first fluidizing bed and thesecond fluidizing bed, wherein the filter is configured to removemoisture from the boriding gas stream.
 14. The assembly of claim 1, andfurther comprising a first heat exchanger in fluid communication withthe first conduit and positioned in fluid connection between the firstfluidizing bed and the second fluidizing bed, wherein the heat exchangeris configured to condense water vapor present in the boriding gasstream.
 15. The assembly of claim 14, and further comprising a secondheat exchanger in fluid communication with the first conduit andpositioned in fluid connection between the first fluidizing bed and thesecond fluidizing bed, wherein the heat exchanger is configured to heatthe boriding gas stream.
 16. The assembly of claim 1, and furthercomprising a mixer in fluid communication with the first conduit andpositioned in fluid connection between the first fluidizing bed and thesecond fluidizing bed, wherein the mixer is configured to mix theboriding gas stream with an inert gas.